1. Technical Field
The present invention is directed toward sailboat rigging, and more particularly toward a vang assembly for manipulating the boom of a sailboat.
2. Background Art
A vang ("kicking strap" to the British) is an adjustable rigging fitted to the underside of a boom to control the raising or lowering of the boom in changing wind conditions.
Vangs are well known in sailing rigging art, and can be divided into three basic types: (1) soft vangs, (2) hydraulic vangs and (3) mechanical vangs. The oldest and most widely used vangs are soft vangs. A soft vang is used to limit twist in a mainsail by placing the mainsail's leech in tension. When a mainsail is eased in medium or heavy air, the boom will lift and the leech will twist and spill wind. Too much twist and the resulting spill of wind reduces the efficiency of the sail and slows the boat. Thus, a soft vang increases sail efficiency by pulling down on the boom in medium or heavy air, thereby increasing the tension in the leech and reducing the spill of wind.
The traditional soft vang is a multi-part rope or wire tackle rigged from the mast base to the underside of the boom with the rope or wire (known as the "fall" in sailing parlance) either secured to a cleat at the mast base or led aft along the cabin top to the cockpit. Soft vangs are generally simple and relatively inexpensive to assemble and install. They are generally used on small and medium size boats.
While soft vangs are extremely effective in maintaining tension in the leech, they have serious limitations. Most importantly, soft vangs may only be used to pull down on the boom. Thus, in slight winds or when docked, a wire or rope topping lift must be used to support the boom. Use of a topping lift is extremely undesirable because it increases the wind drag of the sailboat and has a tendency to chaff the leech.
Hydraulic vangs represent an improvement over soft vangs in that they may both pull down on the boom and hold up the boom, thus eliminating the need for a wire or rope topping lift. Hydraulic vangs typically consist of a cylinder filled with hydraulic oil and a piston. A hydraulic pump controlled from the cockpit actuates the piston inward or outward to control the height of the boom.
Although hydraulic vangs have some advantages over a soft vang (most notably, the ability to hold up the boom) they also have numerous serious drawbacks. First, hydraulic vangs operate under high pressure and therefore require heavy, precisely machined components. Thus, hydraulic vangs are both heavy and expensive. Second, hydraulic vangs are difficult to install, requiring numerous hydraulic connections and conduits. Third, because the vangs are used in a hostile environment, hydraulic vangs must be carefully lubricated and maintained to avoid corrosion and failure. Finally, because of their weight and expense, hydraulic vangs are generally unsuitable for sailboats under 36 feet.
Mechanical vangs are typically similar in appearance to hydraulic vangs but are actuated by mechanical, rather than hydraulic, means.
There are two varieties of mechanical vangs. The first variety is a tackle-equipped rigid vang. These vangs generally comprise a set of telescoping spring-loaded aluminum tubes with a tackle rigging longitudinally associated therewith. When the tackle rigging is tightened, it applies a downward force on the boom and compresses the spring within the telescoping aluminum tubes. As the rigging is loosened, the spring within the telescoping aluminum tubes extends, thus providing support for the boom. Typically, the spring comprises a steel coil; however, compressed-gas cylinder springs are also used.
Tackle-equipped rigid vangs have several serious problems. As with hydraulic vangs, the telescoping tubes must be carefully maintained to avoid corrosion. In addition, if water is allowed to leak into the telescoping tubes, the metal springs may be particularly subject to corrosion. Moreover, the vangs have the undesirable characteristic of squeaking upon slight bobbles at anchor because of the friction between the inside and the outside tube or the spring and the tubes. The telescoping springloaded tubes of these vangs must also be carefully machined, making them relatively expensive. Finally, these vangs are susceptible to denting and bending from transverse forces. Such damage inhibits the telescoping of the tubes, degrading the vang's performance.
The other variety of mechanical vangs are screwdriven or "rotary" vangs. In a screw-driven vang, a large turnbuckle is lengthened or shortened by turning a wheel or a pair of handles in the middle of the turnbuckle. Although capable of providing both tension in the leech and supporting the boom, screw-driven vangs have the serious disadvantage of being difficult and slow to adjust because of their heavy nature.
The present invention is directed toward overcoming one or more of the problems with the prior art discussed above.